An ad libitum NND produces weight loss and blood pressure reduction in centrally obese individuals. This trial was registered at www.clinicaltrials.gov as NCT01195610.

Lipid metabolism is important for health and insulin action, yet the fundamental process of regulating lipid metabolism during muscle contraction is incompletely understood. Here, we show that liver kinase B1 (LKB1) muscle-specific knockout (LKB1 MKO) mice display decreased fatty acid (FA) oxidation during treadmill exercise. LKB1 MKO mice also show decreased muscle SIK3 activity, increased histone deacetylase 4 expression, decreased NAD+ concentration and SIRT1 activity, and decreased expression of genes involved in FA oxidation. In AMP-activated protein kinase (AMPK)α2 KO mice, substrate use was similar to that in WT mice, which excluded that decreased FA oxidation in LKB1 MKO mice was due to decreased AMPKα2 activity. Additionally, LKB1 MKO muscle demonstrated decreased FA oxidation in vitro. A markedly decreased phosphorylation of TBC1D1, a proposed regulator of FA transport, and a low CoA content could contribute to the low FA oxidation in LKB1 MKO. LKB1 deficiency did not reduce muscle glucose uptake or oxidation during exercise in vivo, excluding a general impairment of substrate use during exercise in LKB1 MKO mice. Our findings demonstrate that LKB1 is a novel molecular regulator of major importance for FA oxidation but not glucose uptake in muscle during exercise.

The importance of AMPK in regulation of fatty acid (FA) oxidation in skeletal muscle with contraction/exercise is unresolved. Using a mouse model lacking both AMPKa1 and -a2 in skeletal muscle specifically (mdKO), we hypothesized that FA utilization would be impaired in skeletal muscle. AMPKa mdKO mice displayed normal respiratory exchange ratio (RER) when fed chow or a high-fat diet, or with prolonged fasting. However, in vivo treadmill exercise at the same relative intensity induced a higher RER in AMPKa mdKO mice compared to wild-type (WT = 0.81 6 0.01 (SEM); mdKO = 0.87 6 0.02 (SEM); P < 0.01), indicating a decreased utilization of FA. Further, ex vivo contraction-induced FA oxidation was impaired in AMPKa mdKO muscle, suggesting that the increased RER during exercise originated from decreased skeletal muscle FA oxidation. A decreased muscle protein expression of CD36 (cluster of differentiation 36) and FABPpm (plasma membrane fatty acid binding protein) (by ∼17-40%), together with fully abolished TBC1D1 (tre-2/USP6, BUB2, cdc16 domain family member 1) Ser 237 phosphorylation during contraction/exercise in AMPKa mdKO mice, may impair FA transport capacity and FA transport protein translocation to sarcolemma, respectively. AMPKa is thus required for normal FA metabolism during exercise and muscle contraction.-Fentz, J., Kjøbsted, R., Birk, J. B., Jordy, A. B., Jeppesen, J., Thorsen, K., Schjerling, P., Kiens, B., Jessen, N., Viollet, B., Wojtaszewski, J. F. P. AMPKa is critical for enhancing skeletal muscle fatty acid utilization during in vivo exercise in mice. FASEB J. 29, 1725-1738 (2015). www.fasebj.org Key Words: CD36 • fat oxidation • glucose uptake • physical activity • TBC1D1 GLUCOSE AND FATTY ACIDS (FAs) are the 2 main energy substrates utilized for resynthesis of ATP. The cellular preference for either substrate is influenced by numerous factors, including exercise, diet, and cellular protein expression and activity. Flexibility in the choice of substrate utilization allows organisms to handle metabolic perturbations remarkably efficiently. Impaired flexibility is associated with metabolic diseases in humans (1, 2). Muscle contraction during exercise poses a major metabolic challenge to skeletal muscle and the choice of substrate for oxidation is tightly coupled to the energy turnover.Adenosine monophosphate-activated protein kinase (AMPK) exists as a heterotrimeric protein in both humans and mice and is composed of 1 a, 1 b and 1 g subunit, of which several isoforms exist (a1, a2; b1, b2; g1, g2, g3) (3;4). AMPK is sensitive to decreases in cell energy status (i.e. low ATP and high ADP and AMP) and responds by favoring catabolic and inhibiting anabolic processes to support a continuous provision of ATP. Moreover, AMPK is suggested to play major roles in facilitating skeletal muscle metabolism of both glucose and FA at rest and in response to various hormones and pharmacological agents (4). However, evidence linking the AMPK activation observed during exercise to various processes in FA and ...

The effect of acute inhibition of both mTORC1 and mTORC2 on metabolism is unknown. A single injection of the mTOR kinase inhibitor, AZD8055, induced a transient, yet marked increase in fat oxidation and insulin resistance in mice, whereas the mTORC1 inhibitor rapamycin had no effect. AZD8055, but not rapamycin reduced insulin-stimulated glucose uptake into incubated muscles, despite normal GLUT4 translocation in muscle cells. AZD8055 inhibited glycolysis in MEF cells. Abrogation of mTORC2 activity by SIN1 deletion impaired glycolysis and AZD8055 had no effect in SIN1 KO MEFs. Re-expression of wildtype SIN1 rescued glycolysis. Glucose intolerance following AZD8055 administration was absent in mice lacking the mTORC2 subunit Rictor in muscle, and in vivo glucose uptake into Rictor-deficient muscle was reduced despite normal Akt activity. Taken together, acute mTOR inhibition is detrimental to glucose homeostasis in part by blocking muscle mTORC2, indicating its importance in muscle metabolism in vivo.

To understand the mechanisms in lipid-induced insulin resistance, a more physiological approach is to enhance fatty acid (FA) availability through the diet. Nine healthy men ingested two hypercaloric diets (in 75% excess of habitual caloric intake) for 3 days, enriched in unsaturated FA (78 energy % [E%] fat) (UNSAT) or carbohydrates (80 E% carbohydrate) (CHO) as well as a eucaloric control diet (CON). Compared with CON, the UNSAT diet reduced whole-body and leg glucose disposal during a hyperinsulinemic-euglycemic clamp, while decreasing hepatic glucose production. In muscle, diacylglycerol (DAG) and intramyocellular triacylglycerol were increased. The accumulated DAG was -1,3 DAG, which is known not to activate PKC, and insulin signaling was intact. UNSAT decreased PDH-E1α protein content and increased inhibitory PDH-E1α Ser phosphorylation and FA oxidation. CHO increased whole-body and leg insulin sensitivity, while increasing hepatic glucose production. After CHO, muscle PDH-E1α Ser phosphorylation was decreased, and glucose oxidation increased. After UNSAT, but not CHO, muscle glucose-6-phosphate content was 103% higher compared with CON during the clamp. Thus, PDH-E1α expression and covalent regulation, and hence the tricarboxylic acid cycle influx of pyruvate-derived acetyl-CoA relative to β-oxidation-derived acetyl-CoA, are suggested to impact on insulin-stimulated glucose uptake. Taken together, the oxidative metabolic fluxes of glucose and FA are powerful and opposite regulators of insulin action in muscle.